The present invention relates to a switching device for connections between electric circuits comprising at least one toggle contact element oscillatably movable about a fulcrum between two operating end positions, one operating push-button adapted to exert a command force on said toggle element, said push-button being movable between two control positions corresponding to said two operating positions of the toggle element, and spring means interposed between said toggle contact element and operating push-button and adapted to exert an elastic thrust for locking said push-button to either one of said control positions and said toggle element to a corresponding one of the operating positions thereof.
It is known that switching devices for connections between electric circuits can, depending on their construction mode, perform various different functions, as on-off switches, double-throw switches and the like, for example.
Practically, each of said devices generally has, in addition to fixed contacts necessary for carrying out the intended function and integral with a support structure, a toggle contact element, that is an element oscillatably movable about a fulcrum between two operating end positions, each adapted to create an electric continuity for example, between the toggle element itself and one of the fixed contacts.
Displacement of the toggle element to either one of its operating positions is caused by an operating push-button manually operable between two stable control positions, each corresponding to one of the two operating positions of said toggle element.
The operating push-button, by interposition of appropriate actuator elements and spring means, is caused to exert an elastic command force on the toggle element which, when said toggle element is in its operating positions, is converted into an elastic locking thrust adapted to carry out a mating load between the movable and fixed contacts, which load should never be under a preestablished minimum value.
For example, in a first device of known type, the spring means consists of a spiral spring fitted in the operating push-button and having its longitudinal axis lying in a plane perpendicular to the plane of the toggle element fulcrum. Interposed between the spring, subjected to deformation in terms of shortening and lengthening along its own longitudinal axis, and the toggle element is a thrust element in the form of a ball or a runner which, during displacement of the push-button between its control positions, slides over a portion of the toggle element itself causing it to oscillate from one to the other of its operating positions.
In a second device of known type, the spring means consists of a longitudinal portion of the toggle element itself cut in the form of a blade so that it acts as a leaf spring, that is as a flexible element put into contact with a control finger or pin projecting inwardly from the operating push-button and integral therewith. In this second type of device as well, the end of the control pin, as the push-button is pressed and rotates, slides along the leaf-spring blade exploiting the elastic deformation in a plane transverse to the fulcrum and causes passage of the toggle element to a new operating position.
The known art briefly described above has some important limits and drawbacks.
In fact, first of all, both the above mentioned devices have elements that, by sliding on a portion of the toggle element, cause a friction force thereon of a non-negligible amount and corresponding to the elastic reaction exerted by the spring or the leaf-spring blade. This friction force inhibits an immediate tripping or jumping from one end position to the other of the push-button and therefore of the toggle element operated thereby, so that a user is obliged to press the push-button for some time in order to follow its movement for part of its displacement. Practically, above all after many operating cycles and consequently due to a partial yielding of the elastic elements, in some cases one or more unstable balance positions intermediate the end stability positions of the push-button and related toggle element can occur, thereby producing clear damages from the point of view of the electric operability.
In addition, the mentioned friction force gives rise to wear of the sliding elements in time and therefore limits the efficient operating duration of the device. On the other hand, in the known art it is impossible to select springs or leaf springs of lower elastic stiffness to limit sliding frictions, because electrically appropriate mating thrusts are to be ensured between the movable contact and fixed contacts.
It is to be added that the devices of known type, due to their structural conformation, carry out elastic thrusts of less amount on the toggle element, as the toggle element moves close to its operating end positions. In fact, for example, in the first-mentioned device the spiral spring of the compression type is more elongated at said end positions and therefore in this situation exerts less elastic force. Possible additional pressures on the command key that has already reached a stability end position lead to a further elongation of the elastic element and, instead of increasing the contact or mating force between the contacts, bring about a reduction in said force, that is a partial discharge between the contacts that can even give rise in some cases to formation of sparks and electric arcs.
This situation, which is particularly dangerous, may also occur in the case of devices subjected to vibrations, as it often happens in applications to apparatuses of various kinds which, by causing slight oscillations of the push-button and the toggle element about their operating positions, can give rise to reductions in the contact forces applied through the elastic elements.
From a construction point of view too the devices of known type have a structure which, for the purpose of keeping an assembled condition and therefore being able to be easily transported, requires a complete mounting of all its component parts and in particular the operating push-button. Under some situations this represents a serious limit because in this case it is necessary for said push-button to be selected already during the initial production step and cannot be optionally added in a subsequent time depending on the specific personalization requirements or operating needs.